AND MATERIAL DISCLOSURE STATEMENT
The present invention relates to a methodology for precision cutting of discrete devices such as found, for example, in the MEMS (Micro-Electro-Mechanical Systems) arts. In particular the present invention is directed to the utilization of resin bond and nickel bond dicing blades in a methodology for the dicing of very small discrete devices such as ink jet printheads.
There are many prior art discrete devices which are formed as a plurality of substrates integrally formed in a wafer or the like and which require intermediate cuts and/or separation into individual sub-units as a step in the fabrication process. Examples of such discrete devices and MEMS are ink jet printheads, lasers, magnetic heads, and semiconductor sensor devices. Most, but not all, of the devices are formed in silicon-based wafers. A preferred technique for separating the sub-units is to saw through the wafer in a procedure referred to as "dicing". The device used to perform the cutting is referred to as a dicing blade or dicing saw. For cutting operations requiring high precision (.+-.10 microns) resin bonded or resinold/diamond blades have been preferred, especially in the production of thermal ink jet printheads, because they form precisely placed, smooth chip-less cuts. These resin bond blades have been typically constructed of a resin-diamond blend. For example, a resinold/diamond blade is disclosed in U.S. Pat. No. 4,878,992 incorporated in its entirety for its teaching, which is constructed of a relatively hard, dense resin bonded material and a 60 to 90% concentration of natural or synthetic diamonds. Other resinold/diamond blades and their use are disclosed in U.S. Pat. Nos. 5,160,403, 5,266,528 and 4,851,371 also incorporated in their entirety for their teaching.
These resin bonded or resinold/diamond blades still suffer from performance variability manifested in the asymmetric wear of the blade periphery and shortened blade life due to chipping caused by the forces generated when pieces of silicon or diamond particles loosened from the dicing blade become jammed between the rotating dicing blade and the silicon wafers being cut. The use of natural or synthetic diamonds also adds to the expense and thereby the desirability of limiting wear and extending blade life.
For a thermal ink jet device it is extremely difficult to produce a high quality cut surface on the device, while maintaining a high cut placement accuracy. The accuracy of cut placement is limited by the necessary use of a soft (phenolic resin) bond dicing blade. A resin bond dicing blade provides the necessary cutting quality, without causing chipping and cracking damage to a relatively brittle silicon device. However, the resin bond blade has a number of limitations when used to dice an ink jet device. These limitations include: (1) rapid and (2) uneven blade wear, (3) decreased cut placement accuracy (+/-6 .mu.m @ 1.sigma.) due to both blade bending and abnormal blade wear, and (5) limited feed rate throughput (1-3 mm/sec. Feed rate).
Use of nickel bonded dicing blades overcomes the limitations of resin bonded blades. But, nickel bonded blades have problems of their own. In particular they cannot provide the required cut quality that must be achieved for the proper functioning of an ink jet printhead. Nickel bond dicing blades are used throughout the semiconductor industry in applications where silicon devices need to be diced on wafers. In most applications, the cut quality requirements are driven by a need to minimize cut edge chipping only along the top and bottom surface of the wafers. Many dicing applications like IC chip fabrication can withstand levels of chipping that are unacceptable when applied to dicing thermal ink jet, micro-lasers, or MEMS devices. This is due to the fact that the function of the dicing cut in standard applications is only to separate the devices and any expected chipping can be accounted for in the design of the wafer dicing street width (chip kerf area) and by blade selection. Because of the greater strength of nickel bonded blades they can be used at much greater feed rates for increased throughput. Feed rates for standard wafer dicing operations may approach and even exceed 100 mm/sec., depending on the material being diced. Nickel bond blades also provide excellent cut placement accuracy due to the high strength and low wear rate which provide resistance to bending and uneven blade wear.
With thermal ink jet devices there are two requirements which must be met. The first purpose is of course to separate the devices. However the second and more critical purpose of the cut is to expose and define the ink outlet surface of the die. To achieve this a high quality surface finish is necessary to ensure that uniform ink drop formation generation and directionality when used in the printer. It is critical that chipping is minimized on this surface to prevent misdirection of the ink drop, which thereby degrades print quality. Tests utilizing nickel bond blades has shown that that the surface finish therein provided is not acceptable.
Therefore, as discussed above there exists a need for a technique and methodology which will solve the problem of providing an acceptable surface finish while also providing greater throughput, less rapid and uneven wear, greater cut placement accuracy, and avoid undesirable cut angles. Thus, it would be desirable to solve this and other deficiencies and disadvantages with an improved methodology.